In the manufacture of microelectronic devices, it is now the practice to fabricate recesses or vias to connect multiple levels of conductive (typically metal) layers in a substrate. The multiple metallization layers are employed in order to accommodate higher densities as device dimensions shrink well below one micron design rules. One type of metal film that is widely used as a material for via metallization is copper. Typically, a copper seed layer 12 (see FIG. 2) is sputtered into a via opening 14, and then the via opening 14 is filled by electroplating it with a copper fill layer (not shown). However, one serious disadvantage of sputtering the copper seed layer 12 into the via opening 14 is that the deposition rate of the copper seed layer 12 near the top corners 16 of the via opening 14 will be greater than near the sidewalls 18 and bottom 20 of the via opening 14. This results in an overhang 22 being formed at the top of the via opening 14 which shadows, (i.e., impairs) the copper deposition on the sidewalls 18 and bottom 20 of the via opening 14. This shadowing effect may cause voids 24, or areas of metal discontinuity, to form in the via opening 14, since additional sputter deposition cannot adequately reach the bottom 20 and sidewalls 18 of the via opening 14 due to the overhang 22 at the top of the via opening 14 which tends to block further sputter deposition into the via opening 14.
For high aspect ratio (i.e, greater than 3:1) vias in a microelectronic device, it is very difficult or impossible to sputter deposit a continuous seed layer on the sidewalls and bottom of a via due to the shadowing effect during the sputter deposition process. In other words, the sputtered seed layer will not be continuous within the via. This means that when a copper film is later electroplated to fill the via, the via will exhibit voids in the via fill metallization that can negatively effect the device reliability and performance. Accordingly, it is desirable to form a continuous seed layer upon which to plate a metal fill layer in order to prevent the formation of voids in a high aspect ratio via. The present invention provides such methods and their associated structures.